What was Roosevelt trying to achieve with this speech, particularly with his opening discussion of American history from 1789 to the end of World War 1?

In the first section of his Four Freedoms Speech, President Franklin Roosevelt attempted to put into historical context the dangers of fascism and the ongoing conflicts overseas to the United States. World War Two was already in full swing in Europe and Asia and it was clear to him and many others that the United States could not stay neutral for much longer. However, there were still many that hoped that the United States could stay out of the conflict. With only a few exceptions the country had avoided what George Washington had called "foreign entanglements" in the past. Roosevelt wanted to make it clear that this situation was something unprecedented in world history. That is why he traced the country's history to illustrate the extreme circumstances that faced the United States.
In the speech, President Roosevelt mentioned or eluded to the Civil War, the French Revolution, Maximilian I in Mexico, World War I, the War of 1812, and Napoleon. He brought up all these historical episodes to point out that the United States always rises to the occasion to defend democracy. Furthermore, the looming conflict was different than all these other examples that he mentioned. Never before had the United States engaged a nation bent on world domination. He was arguing that this war was a threat to America's very existence, as he says,

"In like fashion from 1815 to 1914—ninety-nine years—no single war in Europe or in Asia constituted a real threat against our future or against the future of any other American nation."

By placing the events of his time in their historical context, Franklin Roosevelt was making it clear that America was facing unique and perilous circumstances. The United States had risen to the occasion in the past and, Roosevelt was arguing, could do it again.
https://www.ourdocuments.gov/doc.php?flash=false&doc=70&page=transcript

The Four Freedoms Speech was Roosevelt's 1941 State of the Union address. At this time, the United States had not entered World War II.
Roosevelt recalled U.S. history from 1789 to 1914 because he wanted to emphasize that the U.S. had, all through our history, gotten involved in a number of conflicts outside our borders. Although George Washington in his Farewell Address had advised Americans to mind their own business and not get involved in Europe's affairs, Roosevelt knew that the United States would almost inevitably get pulled into the second World War. Therefore, he wanted to position the U.S. as having had a non-isolationist history. He hoped for it to seem natural for our country to involve itself in yet another war.
Roosevelt also used the speech to champion the U.S., and democracy in general, as the guardians of freedoms worldwide. He listed the four freedoms as freedom of speech, of religion, freedom from (economic) want and from fear. These freedoms would have been understood as a rebuke to the tyranny of Adolph Hitler in Germany.